The invention relates to fuel injectors, and more particularly to fuel filters in fuel injectors.
In modern fuel-injected internal combustion engines, electromagnetic fuel injectors deliver fuel to the engine in metered pulses that are appropriately timed to the engine operation. To produce the metered pulses of fuel, electromagnetic fuel injectors typically include a valve member that is actuated by an electromagnetic coil to open and close the fuel valve. When the fuel valve is open, fuel is injected into the air/fuel mixing chamber and then into the combustion chamber to power the vehicle as is commonly understood. Of course, the fuel can also be injected directly into the combustion chamber.
It is desirable to filter the fuel as it enters the fuel injector to help insure the smooth operation of the fuel injector. Primary fuel filters are commonly used to filter debris contained in the fuel and to prevent the debris from getting stuck between the valve needle and the valve seat, which would cause the injector to remain stuck in the: open position. For example, U.S. Pat. Nos. 4,798,329, 5,238,192, 5,330,649, and 5,335,863 disclose various primary fuel filter arrangements in which a fuel filter is located at or near the point at which the fuel enters the fuel injector.
Aside from the debris originally contained within the fuel, the fuel can pick up additional debris as it passes through the fuel injector. This additional debris is produced during the manufacturing of the fuel injector and includes extremely small particles that cannot be completely removed after the manufacturing process is complete. This additional debris is also capable of hampering the proper operation of the fuel injector and should be filtered. Various secondary fuel filters have been used in an attempt to filter the additional debris picked up by the fuel as the fuel travels through the fuel injector.
With known secondary filter assemblies, particulate contaminants within the fuel may pass through the filter or bypass the filter completely to lodge between the valve needle and the valve seat, causing the valve to stick open and deliver fuel to an engine throughout the combustion cycle. This often occurs due to the improper or incomplete seal between the secondary filter and the supporting components of the fuel injector. The poor sealing characteristics can be inherent in the design of the secondary filter, can be caused by improper assembly of the secondary fuel filter in the fuel injector, or can be attributed to a combination of the design and the assembly. Efforts to improve the sealing characteristics have resulted in prior art secondary filter assemblies that are difficult and expensive to manufacture and assemble.
The present invention provides an improved secondary filter assembly for a fuel injector. The secondary filter assembly of the present invention is located as close to the downstream end of the fuel injector as possible to capture substantially all of the additional debris. In light of the downstream location, the design of the secondary filter assembly has been optimized to minimize the pressure drop across the secondary filter, thereby substantially preventing fuel vaporization the could otherwise result in hot restart problems.
In one embodiment of the present invention, the secondary filter assembly includes a tubular filter in the form of a screen that surrounds the needle portion of the needle valve assembly. Fuel is filtered as it passes through the apertures in the needle, just prior to injection. This first embodiment is easier and less expensive to manufacture and assemble than prior art secondary filter assemblies, yet does a substantially better job of filtering particulate and maintaining the proper operation of the fuel injector. One reason for the improvement is that the filter screen is designed to be self-sealing upon assembly. More specifically, the filter includes at least one end that is forced against and deflected by a surface of the needle valve assembly to form a seal between the end of the filter and the needle valve assembly. Preferably, the end of the filter includes a plurality of finger-like tabs that are deflected by the surface of the needle valve assembly to substantially seal and secure the end of the filter to the needle valve assembly.
In a second embodiment of the present invention, the secondary filter is integrally formed in the needle by laser drilling or otherwise forming thousands of small holes directly in the needle itself, thereby-eliminating the need for a separate filter screen surrounding the needle.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.